cutchin43 wrote:Are we allowed to introduce a new villain in our stories? And by that I mean a Batman villain that isn't in the Arkhamverse, not a villain I made up.

Yes you can. You can be really creative, I'd say. You can even make an older Batman and have him fight the Jla or Blight if you want. The Arkham games have to have happened depending on when something transpires, etc.